The present invention relates generally to recording devices, and more particularly to a print head (or an inkjet head) for use with an inkjet printer. In a generic sense, the inkjet printer means a nonimpact printer (i.e.,a printer using no ink ribbon) that prints by jetting ink droplets on printing paper from a nozzle of the inkjet head. The present invention, which is fit for a piezo-type or bubble-type inkjet head, is applicable not only to a single printer unit but also widely to copiers, facsimile units, computer systems, word processors, and combination machines thereof which have a printing function. The piezo-type inkjet head has a mechanism extruding ink by using a piezoelectric element, while the bubble-type inkjet head has a mechanism extruding ink by applying heat.
The inkjet printer attracts increasing attention in recent years by the recent growing demand for recording devices that is capable of not only forming a high-quality image at a high speed but also handling multicolor printing. Among inkjet heads, for instance, those which employ a piezoelectric element have increasingly come into the limelight in recent years due to its excellency in energy efficiency. This type of inkjet head is typically given its structure by joining a pressure chamber plate, a thin film, and a piezoelectric element together in this sequence with an adhesive into a three-layer body, to which a nozzle plate having a nozzle hole is joined. In the pressure chamber plate, a plurality of pressure chambers, ink supply channels corresponding thereto, and a common ink chamber are formed by grooving such a rigid member as glass. The nozzle plate is joined to the three-layer body so that each nozzle hole may be arranged around the midsection of each opening of the corresponding pressure chamber.
The piezoelectric element, which includes an internal electrode and an external electrode, deforms into such a shape as to pressurize the pressure chamber through the thin film when a voltage is applied from the external electrode to the internal electrode, i.e., the piezoelectric element is charged, while restoring the original state when the voltage is eliminated, i.e., the piezoelectric element is discharged. The thin film transmits the deformation of the piezoelectric element to the pressure chamber. Thus, when a voltage is applied from the external electrode to the internal electrode, the piezoelectric element deforms and pressurizes the pressure chamber through the thin film, and ink is thereby ejected from the pressure chamber through the nozzle hole. In order to narrow a pitch between adjacent nozzle holes to form high-resolution images, assignee of this application has already proposed some inkjet heads having a layered structure and using a piezoelectric element divided into a plurality of blocks by grooves.
The foregoing inkjet heads having a layered structure normally form a comparatively thick thermosetting adhesive layer on the thin film. This adhesive layer and the pressure chamber plate are pressurized and heated to cure the adhesive, whereby the thin film is joined to the pressure chamber plate. The comparatively thick adhesive layer not only joins securely the thin film and the pressure chamber together, but prevents an ink leakage out of the pressure chamber, the ink supply channel, and the common ink chamber. In addition, the comparatively thick layer prevents a short circuit caused by contaminations from the head and/or leaked ink penetrating the piezoelectric element.
The bonding method like this, however, may disadvantageously lead to draining of the adhesive into the pressure chamber and/or the ink supply channel upon joining the thin film and the pressure chamber plate together, since the adhesive layer is relatively thick. Such adhesive would reduce the volumes of the pressure chambers and the ink supply channels, and, in some instances, clog up the ink supply channel to block the ink supply to the pressure chamber. In addition, the adhesives drains into and unevenly expands in a plurality of the pressure chambers and/or the ink supply channels, causing the uneven thickness of the adhesive layer. Accordingly, the pressure chamber plate would become too inclined to arrange nozzle holes around the midsection of each opening of the corresponding pressure chamber. This would resultantly vary the ink quantity and the internal pressure value among the pressure chambers, and the inkjet properties (e.g., a quantity and speed of a droplet) would vary among the nozzles, entailing a disadvantage in hardly obtaining a high-quality image.
On the other hand, it is conceivable that the thickness of the adhesive layer between the thin film and the pressure chamber plate is made thin, but this would impair the capability of sufficiently preventing the ink leakage from the pressure chamber, etc.; therefore the method of using a considerably reduced amount of adhesives would not be practicable.